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It is completely natural to have an urge to go to bed when we get sick. Researchers have found that this urge has a definite purpose, at least in fruit flies. In fruit flies, sleep enhances their immune system response and recovery to infection, according to researchers. 

"It's an intuitive response to want to sleep when you get sick," notes Center for Sleep and Circadian Neurobiology research associate Julie A. Williams, PhD, in the press release. "Many studies have used sleep deprivation as a means to understand how sleep contributes to recovery, if it does at all, but there is surprisingly little experimental evidence that supports the notion that more sleep helps us to recover. We used a fruit fly model to answer these questions."

In a series of two related papers, researchers took a conventional approach by subjecting fruit flies to sleep derivation before infecting them with either Serratia marcescens or Pseudomonas aeruginosa bacteria. They observed that both sleep-deprived flies and non-sleep-deprived control group displayed increased sleep after infection. 

They also noted that the pre-infection, sleep-deprived flies had a better survival rate. "To our surprise they actually survived longer after the infection than the ones who were not sleep-deprived," noted Williams.

"We deprived flies of sleep after infection with the idea that if we blocked this sleep, things would get worse in terms of survival. Instead they got better, but not until after they had experienced more sleep."

Sleep deprivation increases activity of an NFkB transcription factor called 'Relish' which is also needed for fighting infection. 

"Taken together, all of these data support the idea that post-infection sleep helps to improve survival," Williams concluded in the press release.

Findings of the study appear online in the journal Sleep.